1. Field of Invention
The present invention relates to a communication device. More particularly, the present invention relates to a communication device which can avoid affecting the radiation efficiency of an antenna.
2. Description of Related Art
A communication device can emit or receive radio waves through an antenna so as to transmit or exchange radio signals. Because radio waves are a type of high-frequency signal, the radio waves energy is regulated in worldwide countries so as to prevent users from affecting or interfering the operation of other radio communication devices. For example, ICNIRP (International Commission on Non-Ionizing Radiation Protection) suggests that a specific absorption rate (SAR) in humans should not exceed 2.0 W/Kg. The SAR in humans refers to electromagnetic wave power absorbed per unit of mass of an organism in a common electromagnetic radiation environment, and uses W/Kg as a unit. In addition, different communication products, such as mobile phones, tablet computers, hand-held access point devices, etc., are applicable to different environments, so that a factor of distance should be considered.
However, decreasing the interference of the radio communication devices to the external may affect the antenna efficacy. Therefore, conventional skills provide various methods to maintain the antenna efficacy simultaneously with decreasing the interference of the radio communication devices. One conventional skill is to use a proximity sensor to sense an approach of a human body. When the sensor detects a human body approaching, energy of radio signal will be controlled to be decreased. Moreover, when the sensor detects no human body approaching, energy of radio signal will be kept constant or be controlled to be increased. In this condition, requirements of decreasing the interference and maintaining the antenna efficacy can be satisfied. However, a conventional proximity sensor has to include a receiver or sensor formed from metal material for sensing a capacitance change generated by the approach of a human body, thereby determining the proximity of the human body. In other words, the antenna efficacy may be affected by the externally-added receiver or sensor, thus resulting in a narrow operating frequency band. Therefore, besides increasing fabrication and design costs, the conventional skill also affect the occupied area of antenna.